Untersuchungen zur Erhöhung der Festigkeit und Oxidationsbeständigkeit von Coat-Mix-Formenmaterial

Prasse, J.; Luhleich, H.; Nickel, Hubertus

Report

FZJ-2016-05706

Untersuchungen zur Erhöhung der Festigkeit und Oxidationsbeständigkeit von Coat-Mix-Formenmaterial

Prasse, J. ; Luhleich, H.FZJ* ; Nickel, H.FZJ*

1990
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte der Kernforschungsanlage Jülich 2374, 124 p. (1990)

Please use a persistent id in citations: http://hdl.handle.net/2128/12578

Report No.: Juel-2374

Abstract: In a study to increase the oxidation resistance of coat-mix(CM)- material, several experiments for SiC-coatings were performed using different initial materials. The wetting angle between the binder coke and the used liquids was measured by the "drop"-method, for which an apparatus was designed and built. All of the liquids used wetted the binder coke and were usable for the infiltration of CM-material. Information from Japan states that successful SiC-coatings on porous materials were obtained by infiltration of a SiC-dispersion. Experiments to infiltrate CM-materials using this method were not successful. An infiltration depth of only severalmicrometers was reached and the pores were partly closed. A simulation of an ideal layer showed that the porosity of the material would be highly decreased, even by a thin layer. In an other case, CM-material was infiltrated by heating the sample in a mixture of SiC and Si powder in which no melt was formed. The silicon was vaporized into the sample and reacted with the carbon of the material .With a high fraction of silicon in the mixture, only the outer surface of the sample was siliconized. In that case, the structure of the material was destroyed and the edges broke. In a mixture with less Si, a higher infiltration depth was reached and the oxidation resistance was increased by 33 %. As a third infiltration method, the CM-material was infiltrated by different Tetraethoxisilan solutions, which formed a SiO$_{2}$-framework through gelation and drying . The SiO$_{2}$ coated CM-samples were heated up thereafter. The SiO${2}$ reacted to form SiC with the carbon of the material. A good solution for coating the CM-material was attempted by evaluation of literature results and characterisation of the gels by examination of the formed glass by measuring small angle x-ray scattering and viscosity. Samples 8 cm in diameter were completly infiltrated in vacuum. After complete gelation, the gel was dried at 850°C. Afterwards, the SiO$_{2}$-layer was converted to SiC at 1650°C. These layers had no influence on the density, porosity, permeability, heat conductivity and strength of the material. The influence of different temperatures, TEOS-solutions and multiple infiltration on the oxidation behavior was characterized by the loss of mass during oxidation. The oxidation resistance was increased up to 30 %. Extensive SEM-examinations showed that $\beta$-SiC-layers about 0,1 $\mu$m thickness were created on the CM-material. Contrary to the layers on binder coke materials, they were not porous and had a good adherence to the CM-material. It could not be proved whether the layer was complete. The surface microstructures of uncoated and coated samples were examined by SEM during the oxidation. The coated sample had a lower edge resistance than the uncoated samples. Complete infiltration and conversion to SiC, an absence of porosity in the layer, good adherence between layer and binder coke and increasing of the oxidation resistance have been achieved. However, the edge resistance and the accuracy of shape of the CM-mold material were decreased by the coating. Therefore the sol-gel method is not usable for coating the CM-material with SiC.

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